let age: number = 18
let myName: string = 'liu'
let isLoading: boolean = false
let a: null = null
let b: undefined = undefined


let numbers: number[] = [1, 3, 5]
let strings: Array<string> = ['a', 'b', 'c']

// 需求：数组中既有 number 类型，又有 string 类型，这个数组的类型应该如何写？
let arr: (number | string)[] = [1, 3, 5, 'a', 'b', 'c']

let arr1: number | string[] = ['a', 'b', 'c']
let arr2: number | string[] = 123

